Underwater optical metrology system

ABSTRACT

Described herein are methods and devices for improved location of any and all underwater structures or equipment installed underwater. In particular, systems are disclosed that combine optical and acoustic metrology for locating objects in underwater environments. The systems allow for relative positions of objects to be determined with great accuracy using optical techniques, and support enhanced location of devices that utilize acoustic location techniques. In addition, location information can be provided by the system even in conditions that make optical metrology techniques impossible or impractical.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/707,204, filed Dec. 9, 2019, which is a continuation of U.S. patentapplication Ser. No. 16/559,005, filed Sep. 3, 2019, now U.S. Pat. No.10,545,233, which is a continuation of U.S. patent application Ser. No.16/031,867, filed Jul. 10, 2018, now U.S. Pat. No. 10,502,829, whichclaimed the benefit of U.S. Provisional Patent Application Ser. No.62/530,747, filed Jul. 10, 2017, the entire disclosures of each of whichare hereby incorporated herein by reference.

FIELD

The present disclosure is directed to methods and systems fordetermining the location of underwater objects, making measurementsbetween objects, and facilitating the positioning of objects underwaterusing optical and acoustical metrology techniques.

BACKGROUND

The accurate placement and monitoring of underwater equipment, such aswellheads, manifolds, risers, anchors, Pipeline End Terminations(PLETS), Blow Out Preventors (BOPs), pumps, touch down points, suctionpiles, chains, slip joints, templates and pipelines is important toensuring the safe and reliable operation of such equipment. However, themethods available in underwater environments are limited when comparedto surface environments. For example, radio frequencies are severelyattenuated in underwater environments, making radio frequency basedlocation systems, such as a Global Navigation Satellite System (GNSS)like the U.S. Global Positioning System (GPS) and the now obsolete longrange navigation (LORAN) systems, unusable at depth. In addition,conventional land survey techniques, for example using theodolites andmeasuring tapes, can be limited by limited visibility, and because theytypically must be operated directly by a human, which may not bepossible or practicable in certain underwater scenarios. As a result,accurately determining the location of equipment and measurementsbetween equipment in underwater environments during installation andsurvey operations is challenging.

Conventional techniques for determining a location underwater caninclude the use of inertial navigation units (INUs). In addition, arraysof acoustic transducers having known locations can be used fordetermining location within or near the array. Although acoustictechniques can provide relative bearing and distance information, theaccuracy and precision of such systems is relatively low. For example,relative locations can at best be determined with an accuracy of severalcentimeters.

More precise location information can be obtained using active opticaltechniques. For instance, underwater lidar systems are available thatcan provide relative location with a precision of several millimeters orless. However, such systems can suffer from limited operational range,particularly in turbid water conditions.

Accordingly, it would be desirable to provide systems and methods thatallowed for reliable and precise determination of location in underwaterenvironments.

SUMMARY

The present disclosure provides systems and methods for determining alocation of objects and measurements between objects underwater. Inaccordance with embodiments of the present disclosure, the systems andmethods utilize a combination of optical and acoustical methodologiesfor determining the locations of objects in an underwater environment.In accordance with at least some embodiments of the present disclosure,a metrology system incorporates a monitoring system that includes alidar device and an acoustic transceiver. In accordance with still otherembodiments of the present disclosure, acoustic transponders areprovided with target indicia and memory for storing locationinformation. The disclosed systems and methods enable the location ofunderwater objects to be determined precisely and reliably by using bothoptical and acoustical methodologies.

A combined system in accordance with embodiments of the presentdisclosure can include one or more metrology systems that eachincorporate an optical metrology instrument, such as a light detectionand ranging system (hereinafter “lidar”) monitoring device. In suchembodiments, the lidar device can be in the form of a scanning lidar,flash lidar, pulsed laser lidar, amplitude modulated continuous wave(AMCW) phase detection lidar, chirped AMCW lidar, amplitude frequencymodulated continuous wave (FMCW) lidar, true FMCW lidar, pulsemodulation code, or other lidar system. Moreover, the lidar system canincorporate a pulsed or modulated continuous wave laser light source.Other embodiments can include a monitoring system incorporating a lasertriangulation, photometric stereo, stereoscopic vision, structuredlight, photoclinometry, stereo-photoclinometry, holographic, digitalholographic, or other device that uses light to sense 3-D space.Scanning lidars can include a single spot scan or multiple single spotscan be scanned. In addition, the one or more metrology systems canincorporate an acoustic transceiver. The acoustic transceiver canoperate at acoustic frequencies to enable the metrology system to locateacoustic transponders or other acoustic emitters, and to communicatewith acoustic transponders or other receiving devices, such as otheracoustic transceivers.

The combined system can also include one or more acoustic transponders.Each acoustic transponder generally includes an acoustic transducer,target indicia, and memory. In general, the acoustic transducer can beoperated to emit an identification signal to identify the associatedacoustic transducer. In addition, the acoustic transducer of an acoustictransponder can be operated to emit a signal that allows a receivingdevice, such as another acoustic transponder or an acoustic transceiverof a metrology device, to determine a range and bearing to the emittingacoustic transducer. In addition, in accordance with embodiments of thepresent disclosure, target indicia can be included to uniquely identifythe associated acoustic transducer. Alternatively, or in addition, thetarget indicia can be configured to identify a location of the acoustictransducer of the acoustic transponder. In accordance with still otherembodiments of the present disclosure, each acoustic transponder caninclude memory, which can be used to store a location of the acoustictransponder.

Methods in accordance with embodiments of the present disclosure includeproviding a plurality of acoustic transponders having target indicia andan acoustic transducer. Dimensional control data concerning therelationship of the target indicia to the acoustic transducer for eachacoustic transponder is recorded prior to placing the acoustictransponders in underwater locations. After placing the acoustictransponders, one or more metrology systems can be placed in underwaterlocations in the vicinity of at least one of the acoustic transponders.The metrology system can be located approximately, for example using anincluded inertial navigation unit, or more precisely, for example usingan optically determined range and bearing relative to a monument orother reference. The metrology system can then be operated to generatepoint cloud data that includes returns from target indicia of at leastone of the acoustic transponders. The location of the acoustictransponder can then be determined from the point cloud data. Inaccordance with embodiments of the present disclosure, the locationinformation can be communicated from the metrology system to theacoustic transponder, and can be stored in the acoustic transponder. Thelocation information stored by the acoustic transponder can becommunicated to other acoustic transponders as part of or as asupplement to conventional range and bearing signals.

Embodiments of the present disclosure provide a combined optical andacoustical locating and positioning system that includes an opticalbased metrology system and acoustic devices or beacons, referred toherein as acoustic transponders. More particularly, the metrology systemcan determine the relative locations of acoustic transponders within afield with great accuracy (e.g., plus or minus several millimeters).This location information can then be passed to the acoustictransponders themselves. The combined use of an optical based metrologysystem and acoustic transponders within a field can allow for accuratepositioning of structures or vehicles within the field, while usingfewer acoustic transponders than might otherwise be necessary, and whileproviding duplicate, complementary positioning signals (i.e. light basedand sound based signals).

Optical targets can be affixed to undersea structures or acousticbeacons to enhance the identification and locating of such structures bya metrology system. The optical targets can be two or three dimensional.The optical targets can be configured in a known relationship relativeto an acoustic transponder and in particular to an acoustic transducerprovided as part of the acoustic transponder, to allow the preciselocation of the acoustic transducer by an optical metrology system. Inaddition, different targets can have different optical characteristics,to allow the different targets to be distinguished from one another bythe metrology system. In accordance with at least some embodiments ofthe present disclosure, the optical targets can vary characteristics ofthe light that is reflected back to the metrology system. Suchcharacteristics can include the intensity, pattern, frequency, phase, orpolarization of the light. In addition, the targets can encodeinformation using barcodes, holograms, human or machine recognitionperceptible indicia, or the like.

Additional features and advantages of embodiments of the presentdisclosure will become more readily apparent from the followingdescription, particularly when taken together with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts an example of an underwater environment in which systemsand methods in accordance with embodiments of the present disclosure canbe employed;

FIG. 2 depicts an underwater environment that includes a monitoring andmetrology systems, monuments, and acoustic transponders in accordancewith embodiments of the present disclosure;

FIG. 3 depicts a metrology system in accordance with embodiments of thepresent disclosure;

FIG. 4 is a block diagram depicting functional components of a metrologysystem in accordance with embodiments of the present disclosure;

FIGS. 5A-5B depict acoustic transponders in accordance with embodimentsof the present disclosure;

FIG. 6 is a block diagram depicting functional components of an acoustictransponder in accordance with embodiments of the present disclosure;

FIG. 7 depicts a monument in accordance with embodiments of the presentdisclosure;

FIG. 8 is a block diagram depicting a monitoring and control station inaccordance with embodiments of the present disclosure;

FIG. 9 depicts an undersea scenario including the use of an acoustictransponder and a geo-located monument in accordance with embodiments ofthe present disclosure;

FIG. 10 is a flowchart depicting aspects of a method of operating acombined system in accordance with embodiments of the presentdisclosure;

FIG. 11 depicts an undersea scenario in which a monument is used to findthe location of a metrology system;

FIG. 12 is a flowchart depicting aspects of a method of operating acombined system in accordance with the scenario of FIG. 11;

FIG. 13 depicts an undersea scenario including the use of multipleacoustic transponders and a geolocated monument in accordance withembodiments of the present disclosure;

FIG. 14 is a flowchart depicting aspects of a method of operating acombined system in accordance with the scenario of FIG. 13;

FIG. 15 depicts an undersea scenario including multiple objects and theuse of multiple acoustic transponders and multiple geo-located monumentsin accordance with embodiments of the present disclosure;

FIG. 16 is a flowchart depicting aspects of a method of operating acombined system in accordance with the scenario of FIG. 15;

FIG. 17 depicts an undersea scenario including multiple acoustictransponders and multiple metrology systems in accordance withembodiments of the present disclosure;

FIG. 18 is a flowchart depicting aspects of a method of operating acombined system in accordance with the scenario of FIG. 17;

FIG. 19 depicts a 3-D target in accordance with embodiments of thepresent disclosure;

and

FIG. 20 depicts a 2-D target in accordance with embodiments of thepresent disclosure.

DETAILED DESCRIPTION

Embodiments of the present disclosure provide systems and methods thatcan be used in connection with the placement of objects in underwaterenvironments. FIG. 1 depicts a drilling and production system 100, whichis an example of an environment in which embodiments of the presentdisclosure can be employed. The drilling and production system 100 caninclude a variety of surface and subsea or underwater components orobjects 102. As examples, and without limitation, these components orobjects 102 can include processing platforms 104, jack-up platforms 108,floating platforms 112, pipelay or other surface vessels 116, pipelines120, risers 124, manifolds 128, wells 130, touch down point 135, suctionpiles or anchors 136, chain 137, slip joints 138 and blowout preventers132. As can be appreciated by one of skill in the art, it isadvantageous to determine and to track the actual locations of thevarious components 102 of the system 100, of natural features, and ofother objects in the vicinity of the system 100. In addition, componentsof the system 100 often need to be positioned with a high level ofaccuracy, to enable intended functions to be performed, to operativelyconnect to other components, and/or to avoid interfering with theoperation of other underwater components.

FIG. 2 depicts an underwater environment that includes a combinedoptical and acoustical locating and positioning system 200, hereinafterreferred to simply as the combined system 200, in accordance withembodiments of the present disclosure. The components of the combinedsystem 200 can include one or more metrology systems 202, target stands222, monuments 226, and acoustic transponders 228. In the example ofFIG. 2, the underwater environment includes components of a drilling andproduction system as depicted in FIG. 1, however, embodiments of thepresent disclosure can be applied to any underwater environment orsystem. In accordance with embodiments of the present disclosure, thecombined system 200 can employ the one or more metrology systems 202,target stands 222, monuments 226, and acoustic transponders 228 invarious combinations to assist in locating natural features or manmadeobjects 102 within an underwater environment, as well as the othercomponents of the combined system 200.

As depicted in the example scenario of FIG. 2, objects 102 within anunderwater environment can include structures or other manmade objectsthat are stationary within or moving through the environment.Determining the actual locations of such objects 102, components of thecombined system 200, and natural features within the environment isimportant to ensuring the safe and reliable operation of equipment,navigation of the environment, maintenance operations, the installationof additional objects, and the like. In accordance with embodiments ofthe present disclosure, the combined system 200 provides opticalcomponents, in combination with acoustical components to assist inlocating and identifying objects 102 and components of the combinedsystem 200 in an underwater environment. As examples, the opticalcomponents of a combined system 200 can include a metrology system 202that utilizes optical instruments, including but not limited to activeoptical instruments, such as a light detection and ranging (lidar)system, optical targets 240 or 244, and visibly distinct features ofunderwater objects 102. Examples of acoustical components of a combinedsystem 200 can include acoustic transceivers associated with a metrologysystem 202 or other component or object 102, hydrophones 248, hydrophonearrays 252, acoustic transponders 228, and acoustic transducers. Inaddition, a combined system 200 in accordance with embodiments of thepresent disclosure can include components that operate using acombination of methodologies. For example, as discussed in greaterdetail elsewhere herein, a metrology system 202 can include an active,optical system capable of measuring a frequency of a vibration of anacoustic transponder 228 emitting an acoustic signal.

The inclusion of optical metrology components within the combined system200 can allow for the locations of objects 102, combined system 200components, and natural features to be determined with a very high levelof precision (e.g. millimeters). The inclusion of acoustical metrologycomponents within the combined system 200 can allow for the locations ofobjects 102 and combined system 200 components to be determined inconditions in which optical techniques are compromised or unavailable,for example due to turbid water conditions. Moreover, the inclusion ofoptic-based and acoustic-based metrology systems provides redundancy,and enables operation in combination with a wider range of complementarysystems. In addition, the combination of techniques allows improvedlocation accuracy, and operation in a wider range of conditions.

As shown in the example scenario of FIG. 2, combined system 200components, including but not limited to metrology systems 202, targetstands 222, monuments 226, and acoustic transponders 228, can bepositioned using various emplacing equipment 210. As examples, acombined system 200 component can be put into position by a crane 212, asubmersible vehicle 216, or a diver 220. In each instance, the combinedsystem component 200 can initially be placed at a location that isunknown or known approximately. The combined system 200 can then beoperated to determine more accurate location information for theacoustic transponder 228. In addition, the combined system 200 canoperate to assist in placing objects 102, and to determining a locationof objects 102 within an environment with reference to previouslylocated acoustic transducers 228, target stands 222, and monuments 226,as discussed in greater detail elsewhere herein.

A metrology system 202 in accordance with embodiments of the presentdisclosure is positioned within an underwater environment. The metrologysystem 202 can be mounted to a stationary platform or structure 224, orcan be carried by a submersible vehicle 216. A metrology system 202 inaccordance with embodiments of the present disclosure can include anactive optical metrology system or instrument that uses light todetermine the relative locations of objects 102, other metrology systems202, target stands 222, monuments 226, acoustic transponders 228, andnatural features in an underwater environment. As can be appreciated byone of skill in the art after consideration of the present disclosure, ametrology system 202 can determine an absolute or georeferenced locationof an object 102, another component of the combined optical andacoustical positioning system, or a natural underwater feature where themetrology system 202 is itself georeferenced or has measured a relativelocation of an object 102 or other component of the combined system 200that is georeferenced.

As can be appreciated by one of skill in the art, a metrology system 202mounted to a stationary platform or structure 224 has an inherentconical field of regard. By incorporating a pan and tilt head in themetrology system 202, the field of regard can be increased to a full360°, or even to over a hemisphere field of regard. As can further beappreciated by one of skill in the art after consideration of thepresent disclosure, a metrology system 202 can be mounted to a movableplatform or vehicle 216, directly or via a pan and tilt head. Asexamples, but without limitation, a moveable platform or vehicle 216 caninclude a frame or cage that is moved by a crane, or a vehicle, such asbut not limited to an autonomous underwater vehicle (AUV), a remotelyoperated vehicle (ROV), a submersible vehicle, or the like. Moreover, amoveable platform or vehicle 216 can be held stationary, for example bylanding the platform or vehicle 216 on the seafloor or other structure,by clamping onto a structure, or by holding it in a hovering mode, whilethe metrology system 202 is in operation. As discussed in greater detailelsewhere herein, a monitoring system component of the metrology system202 can be operated to scan all or portions of an underwater scene todetermine location information.

The acoustic transponders 228 generally operate to provide outputsignals at acoustic frequencies. For example, an acoustic transponder228 can generate an acoustic identification and ranging signal inresponse to receiving an acoustic interrogation signal. An acoustictransponder can additionally receive range information from anotheracoustic transponder 228. In at least some embodiments, an acoustictransponder 228 can also determine an approximate azimuth and elevationangle of an acoustic signal received from another acoustic transponder228 or from an acoustic transceiver provided as part of a metrologysystem 202. The information regarding the relative range or bearing toanother acoustic transponder 228 can all be provided by an interrogatedacoustic transponder 228 in response to the interrogation signal. Inaccordance with still other embodiments of the present disclosure, anacoustic transponder 228 can store information regarding its locationand can provide that information in response to an interrogation signal.These signals can be received by an acoustic transceiver, acoustictransducer, acoustic transponder 228, hydrophone 248, hydrophone array252, or other sensor. An acoustic transponder 228 in accordance withembodiments of the present disclosure can include a visible target 240or 244 or other indicia that can be used to uniquely identify individualacoustic transponders 228. Moreover, the visible target 240 or 244 canfacilitate determining the location of the acoustic transponder 228using optical metrology techniques. Accordingly, the location of anacoustic transponder 228 within an underwater environment can bedetermined by receiving optical signals from the acoustic transponder228 in the form of reflected ambient or transmitted light. An acoustictransponder 228 can be mounted to a tripod 256, a structure or object102 or 204, a target stand 222, a monument 226, a moveable platform orvehicle 216, or the like.

Target stands 222 and monuments 226 can be included as reference points.More particularly, target stands 222 and monuments 226 can include 3-D240 and 2-D 244 targets that enable the location of a target stand 222or monument 226 to be determined using optical metrology techniques.Additionally or alternatively, target stands 222 and monuments 226 caninclude acoustic transponders 228, to enable the location of a targetstand 222 or monument 226 to be determined using acoustical metrologytechniques. In addition, three-dimensional 240 and/or two-dimensional244 targets can be fixed to various objects 102 in the underwaterenvironment, such as components of a drilling and production system 100,for example, pipelines 120, risers 124, manifolds 128, wells 130, touchdown point 135, anchors, suction piles, pin piles, blowout preventers132, or other structures, target stands 222, monuments 226, stationaryplatforms 224, moveable platforms or vehicles 216, or any otherunderwater object. As discussed in greater detail elsewhere herein,these targets 240, 244 are specifically designed to provide controlpoints within an image or within 3-D point cloud data produced by themonitoring system component of a metrology system 202. The inclusion oftargets 240, 244 can facilitate the accurate determination of a targetlocation within an underwater environment.

FIG. 3 depicts a metrology system 202, mounted to a supporting structure224, in accordance with at least some embodiments of the presentdisclosure. The metrology system 202 generally includes a monitoringsystem 304. The monitoring system 304 can comprise active, light basedsystems, such as one or more lidar devices 308, and one or more acoustictransceivers 310. In the illustrated example, the metrology system 202includes two lidar devices 308, each of which is associated with a panand tilt head 312 that can be operated to point the associated lidardevice 308 along a selected line of sight. Alternatively or in additionto a lidar device 308, the metrology system 202 can include otheroptical metrology systems. An acoustic transceiver 310 can operate atacoustic frequencies, to enable the metrology system 202 togeo-spatially locate acoustic transponders 228 or other acoustictransceivers 310 using an acoustic metrology system. The acousticmetrology system can include, for example but without limitation,Ultra-Short Baseline (USBL), Long Baseline (LBL), untethered invertedUSBL, or other acoustic metrology systems.

2-D targets 244 can be mounted to the frame 316 or other components ofthe monitoring system, and 3-D targets 240 can be mounted to the frame316 or other components of the metrology system 202, to facilitateprecisely locating the metrology system 202 within a field.

The supporting structure 224 can comprise a frame 316 that is in turnmounted to a stationary pad, a mud mat, another structure on the seabed,or placed directly on the seabed. The frame 316 can be designed to belowered by a crane from the surface vessel or rig or can be designed tobe deployed via an ROV. The frame 316 can be lowered using a crane lift320. The lift 320 can be connected to the remainder of the frame 316 bya hinge so it lowers after deployment. This allows the lift 320 to dropout of the field of view of the lidar devices 308. The frame 316 canalso include ROV manipulator handles 324 to facilitate positioning theframe 316 using an ROV or AUV. For example, the frame 316 can be placedon a monument 226 or other structure. The bottom of the frame 316 canhave a pin or receptacle, so it can be lowered onto a mating receptacleor pin on a structure to enable precise location and alignment. Inaccordance with other embodiments of the present disclosure, the frame316 may be carried by a vehicle, such as an ROV. In accordance withstill other embodiments of the present disclosure, a metrology system202 can be mounted to a vehicle via a pan and tilt head or can bemounted directly to a vehicle.

In at least some embodiments of the present disclosure, the metrologysystem 202 can itself comprise a subsea system with a platform withnumerous selectable functions. In embodiments in which the metrologysystem 202 includes a support structure or frame 316 that holds multiplelidar devices 308, the lidar devices 308 and acoustic transceiver ortransceivers 310 can be precisely located on the single structure sothey create a single referenced point cloud. By mounting the lidardevices 308 on pan and tilt heads 312, they can provide hemisphericalcoverage. Cameras and lights 328 can be mounted on the support structure316 or the pan and tilt heads 312 to enable the acquisition of visualdata along with the lidar data. A hot stab 332 can be included to enablethe metrology system 202 to connect to the local infrastructure forpower and or communications. The metrology system 202 can furtherinclude one or more non-optical point sensors, such as a conductivity,temperature, and depth (CTD) device 336. Alternately or in addition,batteries and a power control system 340 can be included which allow forlong-term autonomous deployment. The metrology system 202 can alsoprovide additional capabilities including, but not limited to, datastorage and backup, vibration sensors, turbidity sensors, variouschemical sensors, and communication devices. The communication devicescan include RF, optical, or acoustic devices. The communication devicescan communicate with ROVs, AUVs, resident vehicles, other intelligentstructures in the field, or systems on the surface. In accordance withstill other embodiments the metrology system 202 can provide timingsignals (if needed) between multiple sensors to time-synchronize thedata collection of multiple sensors, such as from multiple lidar devices308, and cameras 328, CTD 336, sonars, INU, and other devices. A singlemetrology system 202 can provide power, data storage, and communicationsfor other metrology systems 200 or lidar devices 308, to supportmultiple monitoring points of view within an underwater environment.

FIG. 4 is a block diagram depicting components of a metrology system 202that may be contained within an underwater pressure vessel 402 orco-located with one another in accordance with embodiments of thepresent disclosure. The metrology system 202 includes a monitoringsystem 304. The monitoring system 304 can include a lidar device 308 andan acoustic transceiver 310.

As can be appreciated by one of skill in the art after consideration ofthe present disclosure, a lidar device 308 is an active optical systemthat operates by transmitting light towards a target, receivingreflected light from the target, and determining the range to the targetbased upon time of flight information determined from the amount of timeelapsed between the transmission of light from the light source and thetime at which the reflected light or return signal is received at areceiver. As used herein, a target can include an area or feature on thesea floor, an object 102, or any other underwater structure or feature,including manmade structures and natural features or structures, 3-Dtargets 240 mounted to an underwater structure or device, or placed onthe sea floor, and 2-D targets 244 applied to an underwater structure ordevice, or placed on the sea floor. In addition, the location of a pointon the target from which light is reflected can be located relative tothe lidar device 308 in three-dimensional space by combining the rangeinformation with the known azimuth and elevation information via scannerlocation (e.g. as an azimuth angle and an elevation angle) for scanninglidar devices 308, pixel location for multi-pixel lidar devices 308, ora combination of the two. The fourth dimension, time, is also recordedso measurements and features can be compared over time. As can beappreciated by one of skill in the art after consideration of thepresent disclosure, the lidar device 308 enables the metrology system202 to determine the locations of objects 102 relative to the metrologysystem 202, or relative to objects within the field of regard of thelidar device 308, or that otherwise have a known relative location,using signals at optical frequencies. Moreover, where a reference target240, 244, monument 226, or other object within the field of regard ofthe lidar device 308 has a known absolute location, the lidar device 308can determine the absolute location of the metrology system 202 itselfand of the objects 102 within its field of regard of the metrologysystem 202.

As can also be appreciated by one of skill in the art afterconsideration of the present disclosure, an acoustic transceiver 310 isan acoustic system that can include active and passive acousticcomponents. The active components can provide an acoustic signal thatidentifies the associated metrology system 202, provides informationthat allows an acoustic transceiver provided as part of anotherinstrument or device to determine a relative range and bearing to theemitting acoustic transceiver 310, provides interrogation signals tospecific acoustic transponders 228, performs an acoustic modem function,for example to transmit location information to an acoustic transponder228, and/or the like. The passive components can receive acousticsignals from acoustic emitters provided as part of another instrument ordevice. Accordingly, the acoustic transceiver enables the metrologysystem 202 to identify and to determine the location of acousticemitters relative to the metrology system 202. Where an acoustictransponder 228 or other acoustical emitter has a known absolutelocation, the acoustic transceiver 310 can determine the absolutelocation of the metrology system 202 itself and of other acousticemitters from which the acoustic transponder 228 receives a signal.Moreover, as discussed in greater detail elsewhere herein, a metrologysystem 202 can use optical and acoustic signals in combination to locateobjects 102 in an underwater environment accurately and in a widevariety of conditions.

A metrology system 202 can also include a navigation system, such as anInertial Navigation Unit (INU) 403, which can be used to provideinformation regarding the location of the metrology system 202, and inturn of objects 102 within the field of regard of the lidar device 308or objects 102 from which an acoustic locating signal is received by theacoustic transceiver 310. The INU 403 can be used independently or inconjunction with other metrology systems, including light and acousticmetrology systems, such as acoustic beacons, super-short baseline (SSBL)systems, ultra-short baseline (USBL) systems, untethered inverted USBLsystems, or long baseline (LBL) systems.

The components of the lidar device 308 provided as part of a metrologysystem 202 include a light source 404. The light produced by the lightsource 404 can be collimated or variably focused by optics 408. Inaccordance with at least some embodiments of the present disclosure, thelight source 404 is a pulsed beam laser. As can be appreciated by one ofskill in the art after consideration of the present disclosure, thelight source 404 can produce light having a selected wavelength or rangeof wavelengths. As an example, but without limitation, the light source404 may comprise a blue-green laser light source. As a further example,the light source 404 may have an output centered at 532 nm. Otherwavelengths can also be used, for example to optimize performance inresponse to various water conditions. In accordance with still otherembodiments, the light source 404 may produce non-collimated light. Inaccordance with still other embodiments, the light source 404 may belight emitting diode (LED) based, continuous wave (CW) laser based,modulated CW based, structured light, or some other light source.

The variable focus optics 408 can include traditional mechanicalfocusing elements, or non-mechanical elements, such as may be providedby fluid lenses, liquid crystal devices, electro-optic devices, andother optical elements. The ability to focus the beam can be used tooptimize signal return for a specific target at a specific range forspecific water conditions. The light can then be adjusted in magnitudeby a variable filter or attenuator 412. This is advantageous forunderwater sensing as the attenuation of seawater or other water bodiescan vary dramatically, thus dramatically changing the return signal,which can strain the dynamic range of the receiver. One method forreducing the required dynamic range of the receiver is to adjust thelight output power from the transmitter. This can be achieved by thevariable attenuator 412. As examples, the variable attenuator 412 caninclude standard neutral density filters, other attenuation filters, orpolarization elements.

The optical train can also include a variable polarization rotator 416.It is known that the polarization of the transmitted light can affectthe backscatter power, which is a source of noise at the lidar device308 receiver. Transmission range can therefore be optimized by adjustingthe polarization rotation of the output light. The variable polarizationrotator 416 can impart any polarization to the output light.

Transmit and receive (Tx/Rx) optics 420 are used to make the sensormonostatic. Monostatic sensors have the distinct advantage of simplifiedscanning as the transmitter and receiver are pointed at the samelocation with the same scanning mechanism, resulting in calibration andreliability performance that is superior to bistatic systems. A scanningdevice 424 can then be used to accurately direct the transmitted beamand the field of view of the receiver simultaneously to a scene througha window 428 in the enclosure 402. The scanning device 424 can include asteering mirror or other beam steering device, such as amicro-electro-mechanical system (MEMs), liquid crystal, acousto-optic,or electro-optic device, for precise control of the pointing of thelight source and receiver toward a target location 202, such as anunderwater structure, and at known angles relative to the metrologysystem 202.

Light reflected from the target is received by the scanning device 424and is split by a beam splitter element included in the Tx/Rx optics420. Light from the Tx/Rx optics 420 is provided to a receive telescope430, which is configured to focus the received light so that it can beimaged onto the sensor elements of a receiver 444 included in themetrology system 202. In a different embodiment the receive telescope430 collimates the light and it is then focused by focusing optic 446. Avariable polarization rotator 432 can be included to optimize thesignal-to-noise ratio (SNR) of the return signal by selecting theoptimal polarization for the hard target return.

A fast shutter 436 is provided to block any stray light from the primarybeam as it exits the window 428, after being directed by the scanningdevice 424. The fast shutter 436 is timed with high speed electronics,which may be implemented by a processor 448, to block the window 428reflection from a transmitted pulse and then open quickly to capturereturns from close targets. Light passed by the fast shutter 436 is thenprovided to the receiver 444. The receiver 444 detects the lightreflected from a target, and timing and intensity information regardingthe received signal is used to create 3-D point cloud data. The receiver444 thus is an optical sensor or detector, such as a photodiode, anavalanche photodiode, a photomultiplier tube, a silicon photomultipliertube, a Geiger mode avalanche photodiode, charge coupled device (CCD)detector, complementary metal oxide semiconductor (CMOS) detector, orother optical detector. It can also include an electronic amplifierand/or thermal control elements and circuitry. In addition, the receiver444 can include or be associated with a narrow band filter to reducebackground light. A focusing optic 446 can be included to focus receivedlight onto the sensor of the receiver 444. In accordance withembodiments of the present disclosure, the receiver 444 may comprise asingle or multiple pixel sensor. Information regarding the range to thetarget is monitored by a processor 448, which controls and/or has accessto information regarding the time at which transmitted light is output,and the time at which a return signal, comprising transmitted light thathas been reflected from a target, is received by the receiver 444. Inaddition, information from the scanning device 424, from a pan and tilthead 312, from a pitch and roll sensor 426 mounted to the pan and tilthead 312 or included in the lidar device 308, and/or the location of areceiving pixel in a lidar device 308 having a multiple pixel sensor asthe receiver 444 can be used by the processor 448 to determine theazimuth angle and elevation angle to the target. This information canthen be combined with timing information, and in particular the time atwhich the transmitted pulse of light produced by the light source 404 issent towards the target, and the time that the return signal is receivedat the receiver 444. The range measurement determined from the timinginformation can then be applied to obtain a location of the targetrelative to the metrology system 202. The pitch and roll sensor orsimilar device can be used to provide the gravity vector of the pointcloud. This can then be used to orient the point cloud in relation togravity, thus in effect “leveling” the system.

The acoustic transceiver 310 generally includes an acoustic output ortransmitter 405 and an acoustic input or receiver 406. As examples, butwithout limitation, the acoustic transmitter 405 may comprise anacoustic transducer or set of transducers that operate to transformelectrical signals into acoustic signals having a selected frequency orfrequencies, and to transmit that frequency or set of frequenciesthrough the water surrounding the metrology system 202. Moreover, asignal output by the acoustic transmitter 405 can be encoded, forexample to address a specific acoustic transponder 228 or set oftransponders 228, or to signal an acoustic transponder 228 to output areply or identification signal, to transmit location information for anacoustic transponder 228 or to another combined system 200 component, orto otherwise perform an acoustic modem function. The acoustic receiver406 may comprise a hydrophone or set of hydrophones that operate toreceive acoustic signals from the water surrounding the metrology system202 and to transform those signals into electrical signals. As discussedin greater detail elsewhere herein, received acoustical signals caninclude identification, acknowledgement, ranging, communication, orother signals. The acoustic transceiver 310 can be inside the sameenclosure 402 or can be outside enclosure 402 and contained within itsown enclosure, which is generally a pressure housing.

The processor 448 can include any processor capable of performing orexecuting instructions encoded in system software or firmware 463 storedin data storage or memory 464, such as a general purpose programmableprocessor, controller, Application Specific Integrated Circuit (ASIC),Field Programmable Gate Array (FPGA), or the like. Moreover, theexecution of that software or firmware 463 can control the operation ofthe metrology system 202.

With respect to the lidar system 308, operation of the metrology system202 can include the acquisition of point cloud data that includesazimuth angle, elevation angle, intensity, and range information takenfrom an underwater scene comprising the area surrounding the metrologysystem 202, and can further include the identification of objects 102,targets 240 and 244, and the like within the scene. With respect to theacoustic transceiver 310, operation of the metrology system 202 caninclude the interrogation of acoustic transponders 228 within the scenecomprising the area surrounding the metrology system 202, theacquisition of identification, range, bearing or other information, orother operations.

In accordance with embodiments of the present disclosure, theinformation from or about objects 102 within a scene can be obtainedusing both optical and acoustical methodologies, and used selectively orin combination by the metrology system 202 to identify objects within ascene and determine the relative locations of the objects 102. Moreover,where absolute or georeferenced location information is available forthe metrology system or an object 102, a metrology system 202 inaccordance with embodiments of the present disclosure can operate byusing optical and acoustical methodologies alone or in combination togeoreference some or all of the objects 102 within the scene. Moreover,the identification and locating of objects 102 within the scene usingone or more of the methodologies available to the metrology system 202can be performed through operation of the software 463 stored in thememory 464 and executed by the processor 448 provided as part of themetrology system. In accordance with still other embodiments of thepresent disclosure, the metrology system 202 can report data regardingthe identities and locations of objects 102 within a scene, and canexchange information with other metrology systems 202, to exchangeinformation with a user interface, server system, or other computingnode in communication with the metrology system, or the like.

Different operations of the software 463 can be distributed amongstdifferent programs, applications, or software modules. In general, theexecution of the software 463 by the processor 448 can be performed inconjunction with the memory 464. Moreover, the function of the memory464 can include the short or long-term storage of timing information,range information, point cloud data generated by the lidar system 308,control point locations, or other control information or generated data.The memory 464 can comprise a solid-state memory, hard disk drive, acombination of memory devices, or the like.

The metrology system 202 can additionally include various sensors, inaddition to those included in the lidar system 308 and the acoustictransceiver 310. For example, the metrology system 202 can include a CTDdevice 336 for measuring the conductivity (and thus the salinity), thetemperature, and the depth of the water at the location of the metrologysystem 202. Because a CTD device 336 must be in direct contact with thesurrounding water, it can be mounted outside of or adjacent an aperturein the enclosure 402.

Embodiments of the present disclosure can include all of the componentsillustrated in FIG. 4, additional or alternate components, or a subsetof these components. In accordance with embodiments of the presentdisclosure, the range and angle measurements made by the lidar system308 should all be compensated using techniques described in U.S. Pat.Nos. 8,184,276 and 8,467,044. The memory 464 can be used for storing thelocation information, operating instructions, generated data, and thelike. An input/output or communication interface 468 can be included fortransmitting determined information to a monitoring and control station804 (see FIG. 8) or other system or control center in real-time, nearreal-time, or asynchronously. A power source and distribution bus 472can also be integrated with the metrology system 202. Various elementsof a metrology system 202 as disclosed herein can be provided as or bydiscrete or integrated components. For example, various optical elementsof the lidar system 308 can be formed on a substrate that is bonded tothe semiconductor substrate in which the receiver 444 is formed,creating an integrated chip or package.

FIG. 5A depicts an acoustic transponder 228 in accordance withembodiments of the present disclosure. As shown in the figures, anacoustic transponder 228 as disclosed herein generally includes a watertight body or housing 504 to which one or more 2-D targets 244,identifying codes, letters, or numerals 508, or other indicia 512 havebeen applied. In addition, the acoustic transponder 228 includes anacoustic transducer 516. As can be appreciated by one of skill in theart, the acoustic transducer 516 is located so that it is in contactwith the surrounding water when the acoustic transponder 228 is in placein an underwater location. As described in greater detail elsewhereherein, the indicia 512 can be configured to uniquely identify anassociated acoustic transponder 228, and to assist in precisely locatinga reference point 520, such as a physical center point, of the acoustictransducer 516 using optical instruments, such as a lidar system 308included as part of a metrology system 202 as disclosed herein. Inaccordance with still further embodiments of the present disclosure, theindicia 512 can include a 2-D target 244 that is applied directly to thesurface of the acoustic transducer 516. Accordingly, instead of thegenerally poorly reflective, rubber or other pliable surface of thetypical acoustic transducer 516, a highly reflective target 244 can beapplied to a portion of that surface, facilitating the identification ofthe location of the acoustic transducer 516 using a lidar device 308 orother optical system.

In the embodiment depicted in FIG. 5A, the targets 244 are applieddirectly to the housing 504. As depicted in FIG. 5B, targets 244 can beheld on arms 524 that extend from the housing 504, as well as or inplace of targets 244 applied to the housing 504. Alternatively or inaddition, a 3-D target 240 can be fixed to the housing 504. As can beappreciated by one of skill in the art after consideration of thepresent disclosure, the inclusion of one or more 3-D targets 240 and/orof one or more targets 244 held on arms 524 allows the targets 240 or244 to be positioned at greater distances from one another, therebyincreasing the ability of the metrology system 202 to identify thelocation of the center point 520 of the acoustic transducer 516 includedin the associated acoustic transponder 228. The additional targets 240and/or 244 included on the arms 524 can also provide more control pointsin different orientations and planes for transponder 228 than can beprovided on the housing 504 itself. In accordance with still otherembodiments, an acoustic transponder 228 can be fixed to a target stand222 and can be located precisely with reference to targets 240 or 244also fixed to the target stand 222. A target 244 can also be placeddirectly on the acoustic transducer 516 at a location corresponding tothe center point 520 of the acoustic transducer 516.

All reference indicia 512 and optical targets 240 and/or 244 can bemeasured with high accuracy in 3D space at the surface (in air) relativeto the center or reference point 520. These dimensional control (DC)offsets can then be used to identify the location of the reference point520 underwater with high accuracy based upon reference indicia 512 andthe targets 244 or 240. Identifying codes, letters, or numerals 508 caninclude a bar code type system that the lidar device 308 or otheroptical system automatically reads. The system can then use a databaseor other method to identify the unique transponder 228 and acquire theDC offsets or other metadata for the uniquely identified transponder 228from the database. In addition, to the DC offsets, the metadata caninclude hub number, date of installation, acoustic identification code,or any other information associated with the transponder 228. Thisreduces the need for ROV video identification.

FIG. 6 is a block diagram depicting components of the acoustictransponder 228 of FIGS. 5A-5B. These components generally include thehousing 504, the acoustic transducer 516, a processor 604, memory 608,and a power supply 612. Note that the acoustic transducer 516 can be asingle transducer or an array of individual transducers, where the arrayallows for direction finding. The processor 604 may comprise a generalpurpose programmable processor or controller that is capable ofexecuting software or firmware, such as, but not limited to, anapplication 616 stored in memory 608. The application 616 may compriseinstructions controlling the operation of the acoustic transponder 228,such as identifying acoustic interrogation signals that are received atthe acoustic transducer 516 and are addressed to or that otherwiserequire a response or other action by the acoustic transponder 228. Theapplication 616 can further operate to cause the acoustic transducer 516to output an acoustic identification, ranging, direction, or othersignal, for example periodically or in response to an interrogationsignal. In addition to an application 616, the memory 608 of theacoustic transponder 228 can store identification codes, rangingsequences, or other data 620. An acoustic transponder 228 in accordancewith still other embodiments of the present disclosure can operate tostore information in memory 608 regarding the location of the acoustictransponder 228, for example that has been communicated to the acoustictransponder 228 as part of an acoustic information signal provided by ametrology system 202 that has determined that location information. Insuch embodiments, the acoustic transponder 228 may further operate totransmit its location information to other acoustic transponders 228, toacoustic transceivers 310, or other devices. An acoustic transponder 228can additionally implement an acoustical modem function to send, relay,or receive information encoded on acoustic carrier frequencies.

FIG. 7 depicts a monument 226 that can be used in connection withdetermining locations of objects 102 and underwater features as part ofa combined system 200 as described herein. The monument 226 featuresthree-dimensional 240 and/or two-dimensional 244 targets. In accordancewith further embodiments, the monument 226 can include additional orreference indicia 512, such as scales 704, identifying codes, letters,or numerals 508, or the like. Such indicia 512 can assist in visuallyidentifying the monument 226 and the relative location of the monument226, for example using a lidar 308 provided as part of a metrologysystem 202. A monument 226 can therefore provide a reference point withrespect to which the relative location of an underwater structure orobject 102, target stands 222, acoustic transducers 228, and/or themetrology system 202 itself can be determined and monitored. Inaccordance with still further embodiments of the present disclosure, themonument 226 can include an acoustic transponder 228 to enable theacoustic validation of the location of the monument 226, and to provideacoustic relative location data. The acoustic transponder 228 caninclude targets 244 or other indicia 512, an acoustic transducer 516,and other components included in an acoustic transponder 228 generally.Moreover, the acoustic transponder 228 can receive and store informationregarding the location of the acoustic transponder 228 and/or theassociated monument 226, and can communicate that information to othercombined system 200 components, such as other acoustic transducers 228and acoustic transceiver 310 components of metrology systems 202. Theinclusion of an acoustic transponder 228 as part of or mounted to amonument 226 therefore allows for an independent location validationmeasurement using a different measurement mechanism (acoustic versusoptical). Accordingly, one or more monuments 226 can be positionedwithin a scene to provide fixed reference points that can be accuratelyidentified by the metrology system 202 and that can be used as referencepoints to determine the location of underwater structures 102, acoustictransponders 228, metrology systems 202, or other objects within theunderwater scene relative to the monuments 226.

FIG. 8 is a block diagram depicting human interface and other componentsthat can be provided as part of or in conjunction with a monitoring andcontrol station 804 associated with a combined system 200 in accordancewith embodiments of the present disclosure. The monitoring and controlstation 804 can be provided as a top-side facility, carried by a mobileplatform, such as a surface ship or a submersible vehicle, mounted to afixed or stationary platform, such as a production platform, or locatedat an on-shore facility. The monitoring and control station 804facilitates or performs functions that include providing output to andreceiving input from a user or from an automated processing center. Themonitoring and control station 804 generally includes a processor 808and memory 812. In addition, the monitoring and control station 804 caninclude one or more user input devices 816 and one or more user outputdevices 820. The monitoring and control station 804 also generallyincludes data storage 824. In addition, a communication interface 828can be provided, to support interconnection of the monitoring andcontrol station 804 to the underwater components of the combined system200, and/or to other systems. This interface can be used as a commandand control interface to another autonomous device that provides theinputs and reads outputs that replaces human user interfaces 816 and820.

The processor 808 may include a general purpose programmable processoror any other processor capable of performing or executing instructionsencoded in software or firmware. In accordance with other embodiments ofthe present disclosure, the processor 808 may comprise a controller,FPGA, or ASIC capable of performing instructions encoded in logiccircuits. The memory 812 may be used to store programs and/or data, forexample in connection with the execution of code or instructions by theprocessor 808. As examples, the memory 812 may comprise RAM, SDRAM, orother solid-state memory. In general, a user input device 816 isincluded as part of the monitoring and control station 804 that allows auser to input commands, including commands that are transmitted to theunderwater components of the combined system 200, and to control aspectsof the operation of the metrology system 202. Examples of user inputdevices 816 that can be provided as part of the monitoring and controlstation 804 include a keyboard, keypad, microphone, biometric inputdevice, touch screen, joy stick, mouse, or other position encodingdevice, or the like. A user output device 820 can, for example, includea display, speaker, indicator lamp, or the like. Moreover, a user inputdevice 816 and a user output device 520 can be integrated, for examplethrough a graphical user interface with a pointing device controlledcursor or a touchscreen display. Like the memory 812, the data storage824 may comprise a solid-state device. Alternatively or in addition, thedata storage 824 may comprise, but is not limited to, a hard disk drive,a tape drive, or other addressable storage device or set of devices.Moreover, the data storage 824 can be provided as an integral componentof the monitoring and control station 804, or as an interconnected datastorage device or system.

The data storage 824 may provide storage for a subsea monitoring systemapplication 832 that operates to present a graphical user interfacethrough the user output device 820, and that presents a map or otherrepresentation of the locations of objects 102, metrology systems 202,target stands 222, monuments 226, acoustic transponders 228, and/orother objects in an underwater environment. The presentation can furtherdepict any differences between the location of an object 102 asdetermined using a lidar device 308 and a location as determined by anacoustic transceiver 310. For instance, as an optically determinedlocation, when available, is typically more precise than an acousticallydetermined location, a location as determined by the optical system canbe represented as a point on a map of the seafloor, while the locationas determined by the acoustical system can be represented by an area onthe map. This can include visual representation of measurementuncertainty, or error bars, of each measurement system. The outputdevice 820 can further provide a view of point cloud data 840, or dataderived from point cloud data, obtained by a metrology system 202. Theapplication 832 can further operate to receive control commands from auser through the user input device 816, including commands selectingtarget areas or specific targets within an underwater scene from which3-D point cloud data should be obtained by the metrology system 202.Moreover, the application 832 can operate to receive control commandsregarding acoustic transponders 228 that should be interrogated, andfrom which location information should be collected. In accordance withembodiments of the present disclosure, the application 832 can performvarious functions autonomously, such as identifying underwater objects102, such as target stands 222, monuments 226, acoustic transponders228, identifying features on underwater objects 102, identifying acentroid of an underwater object or a feature of an underwater object,identifying control points on underwater objects, identifying target 240or 244 centroids, monitoring the motion, and/or vibration of underwaterobjects, or other operations. Such automated operations can beimplemented using, for example, image recognition techniques. The datastorage 824 can additionally provide storage for the identifiedlocations of underwater objects 102, control point data 836, point clouddata 840, maps of underwater features, identifiers of underwaterfeatures, indicia 512 and identification codes of acoustic transponders228, and the like. In accordance with still other embodiments of thepresent disclosure, the system application 832 can be executed tooperate a metrology system 202 to detect motion, vibration, vibrationmode, changes, features, lack of features, other anomalies,temperatures, or leaks instead of or in conjunction with execution ofthe system software 463 by the processor 448 of the metrology system202. The data storage 824 can also store operating system software 844,and other applications or data.

FIG. 9 depicts an undersea scenario including the use of an acoustictransponder 228 in accordance with embodiments of the presentdisclosure. FIG. 10 is a flowchart depicting aspects of a process thatcan be performed in connection with a scenario such as the oneillustrated in FIG. 9. The first step, which is performed at thesurface, is to take Dimensional Control (DC) data for the acoustictransponder 228 (step 1004). This entails taking highly accuratemeasurements from the actual acoustic element 516 of the transponder 228to the multiple indicia 512 in 3D space (X, Y, Z coordinates). Highlyaccurate measurement can be performed using a Total Station or aCoordinate Measuring Machine (CMM). Less accurate measurements can beachieved with a tape measure or similar device. The measurement canlocate a centroid or defined center point 520 of the acoustic transducer516 relative to the indicia 512. With this information the metrologysystem 202 can accurately locate indicia 512 in 3-D space and then usethe DC offsets to compute the location of the center 520 of the acoustictransducer 516. In accordance with further embodiments of the presentdisclosure, the indicia 512 can include information uniquely identifyingan associated acoustic transponder 228. In this manner the uniqueoffsets for each transponder can be applied.

The acoustic transponder 228 is then lowered and placed in the field 100at an approximately known location (step 1008). The metrology system 202is also lowered and placed in the field 100 at an approximately knownlocation (step 1012). The metrology system 202 can be placed on asupport structure 224, placed on the seabed, carried by an ROV or AUV216 that is stationary on the seabed, carried by an ROV or AUV 216 thatis floating in a station-keeping mode, or otherwise carried or placed inthe vicinity of the acoustic transponder 228.

The next step is to locate metrology system 202 in relation to the field100 (step 1016). Information regarding the location of the metrologysystem 202 can be provided by the INU 403. Alternatively, or inaddition, the metrology system 202 can obtain information regarding itslocation by referencing one or more geo-located monuments 226, targetstands 222, 3-D targets 240, or 2-D targets 244 or other stationarystructures or indicia on the seabed, or even by the seabed featuresthemselves. Location information obtained relative to the geo-locationmonuments 226 or other structures or indicia can replace or besupplemented by the known location of the metrology system 202,obtained, for example, from an INU 403, or other stationary structureson the seabed such as manifolds 128, wells 130, or suction piles 136, oreven by the seabed features themselves. Note the location can begeo-referenced or can be relative to the locations of the monuments 226,or other structures or objects 102 on the seabed.

As shown, the geo-located monument 226 can include indicia 512, such asa two-dimensional 244 and three dimensional 240 targets, acoustictransponders 228, and scales to assist in determining the relativelocation of the metrology system 202, a nearby acoustic transponder 228,or other objects 102. In accordance with further embodiments of thepresent disclosure, the indicia 512 can include information uniquelyidentifying an associated geo-located monument 226.

The metrology system 202 is then used to create a 3D point cloud thatincludes the acoustic transponder 228 (step 1020). With a known locationof metrology system 202, this point cloud can be put in global orgeoreferenced coordinates so the location of indicia 512 on the acoustictransponder 228, and thus the location of the transponder 228, is knownin georeferenced X, Y, Z space (step 1024). In an additional embodiment,the point cloud includes both the acoustic transponder 228 and themonument 226. The relative location of the acoustic transponder 228 isthen determined in 3D space (X,Y, Z coordinates) with respect tomonument 226. The DC offsets for the exact acoustic transponder 228 canthen be applied to identify the location of the acoustic transducer 516in 3D space (step 1028). The process can then end.

FIG. 11 depicts an undersea scenario in which a monument 226 or otherstructure 102 is used to find the location of the metrology system 202.FIG. 12 is a flowchart depicting aspects of the process that can beperformed in connection with the scenario of FIG. 11. Initially, atleast three control points or targets 244 on the monument 226 arecoordinated or georeferenced (step 1204). The at least three previouslycoordinated reference points or targets 244, are shown as points A, B,and C in FIG. 11. The metrology system 202, in this example carried byan underwater vehicle 216 in the form of an ROV, is placed at a locationfrom which the targets 244 on the monument 226 are visible, to enablethe metrology system to determine its location relative to the targets244 (step 1208). More particularly, the lidar device 308 included in themetrology system 202 is operated to scan the targets 244 (step 1212).The centroids of the targets 244 are then located, for example byoperation of an image analysis module included in the applicationsoftware 463 (step 1216). The location of the metrology system relativeto the targets 244 can then be determined, for example by performing athree point resection traverse, in which the location of the metrologysystem 202 is calculated from the determined angles subtended by linesof sight from the metrology system 202 to the previously coordinatedtargets 244 (step 1220). Moreover, where the monument 226 is itselfgeolocated, determining the location of the metrology system 202relative to the monument 226 allows the metrology system 202 to itselfbe geolocated. Having identified its location relative to a monument 226having a known location, the metrology system 202 can preciselydetermine the location of other objects 102, including but not limitedto other monuments 226, target stands 222, and acoustic transponders228.

FIG. 13 depicts an undersea scenario including the use of multipleacoustic transponders 228 and one or more geo-located monument 226 orother stationary structures on the seabed, or even the seabed featuresthemselves in accordance with embodiments of the present disclosure. Inthis scenario, the multiple acoustic transponders 228 can each includeindicia 512 in the form of reference targets 240 or 244. Informationregarding the X, Y, Z location of the acoustic transponders 228 can beprovided from the metrology system 202 to the transponders 228themselves, which can result in the transponders 228 having improvedlocation accuracy as compared to transponders 228 that rely solely onacoustic information exchanged with other transponders 228. Moreparticularly, and with reference now to FIG. 14, the dimensional controldata, including the relationship between targets 240 and/or 244 and thecenter point 520 of the acoustic transducer 516 for each of the acoustictransducers 228 can be taken (step 1404). The dimensional control datacan be taken on the surface, before the acoustic transponders are placedon the seabed, and can be stored, for example in data storage 824 of amonitoring and control station 804 of the combined system 200. Theacoustic transponders 228 can then be placed on the seabed (step 1408).The metrology system 202 can then be placed such that the acoustictransponders 228 and a previously placed monument 226 with coordinatedtargets 240 and/or 244 are in view of the metrology system (step 1412).The metrology system 202 can then be operated to determine the locationof one or more of the acoustic transponders 228 relative to the monument226 using the included lidar device 308 (step 1416). The preciselydetermined location of an acoustic transponder 228 can then be providedto that acoustic transponder 228, where the location information can bestored (step 1420). The location information can be relative to themonument 226 or can be a georeferenced location. In accordance with atleast some embodiments of the present disclosure, the location for aparticular acoustic transponder 228 determined by the metrology system202 is communicated to that acoustic transponder 228 using an acousticcarrier signal generated by an acoustic transceiver 310 included in themetrology system 202.

Acoustic transponders 228 can then relay their location information toeach other, together with a conventional acoustic locating signal (step1424). This can enable a combined system 200 in accordance withembodiments of the present disclosure to provide location informationwith enhanced precision as compared to systems that do not include theoptically determined location of a transmitting acoustic transponderwith conventional ranging information or range and directioninformation. In particular, if an acoustic transponder 228 is given itsX,Y,Z, roll, pitch, yaw location from a metrology system 202, and thenreceives the location of another transponder 228, it knows the exactrange and location of the other acoustic transponder 228. The range canbe compared to its acoustic range for that acoustic transponder 228.This can be used as a critical quality control check for the rangebetween acoustic transponders 228. Moreover, in this scenario the tworanges are calculated using different sensor physics (acoustic andoptical), providing for a very robust system. For example, the X, Y, Zlocation information of the acoustic transponders 228 can be providedwith millimeter accuracy, as compared to the centimeter to meteraccuracy that is available using acoustic range information alone.Moreover, by combining light based and sound based locatingmethodologies, the ability to obtain a relative range informationbetween nodes of the system or field under different environmental orfailure conditions can be improved as compared to scenarios utilizing asingle methodology for obtaining such information. In accordance withfurther embodiments of the present disclosure, the indicia 512 caninclude information uniquely identifying an associated acoustictransponder 228. This can include a bar code type system that theoptical system, such as the lidar device 308, automatically reads. Thesystem 200 can then use a database or other method to identify theunique transponder 228 and acquire the DC offsets or other metadata froma database. This reduces the need for ROV video identification.

In additional embodiments, the location data of acoustic transponders228 as determined by a metrology system 202, and the acoustic range datacollected by acoustic transponders 228, can both be sent to a localprocessing center or a topside processing center 804 to process andcompare the location data using the two methods.

FIG. 15 depicts an undersea scenario encompassing a field that includesmultiple undersea structures or other objects 102, multiple acoustictransponders 228 and multiple geo-located monuments 226 in accordancewith embodiments of the present disclosure. As depicted in FIG. 16, inthis scenario indicia 512 is applied to the acoustic transponders 228,and DC data is collected from the relationship of the indicia 512 to theacoustic element or transducer 516 of each transponder 228 (step 1604).Each acoustic transponder 228 is also uniquely marked so the unique datafor each acoustic transponder 228 is captured. This can include a barcode type system that the optical system or lidar device 308automatically reads. The system 200 can then use a database to identifythe unique transponder and acquire the DC offsets or other metadata froma database. This reduces the need for ROV video identification. Theacoustic transponders 228 are then lowered and placed in the field 100at approximately known locations (step 1608). A metrology system 202 isalso lowered and placed in the field 100 at an approximately knownlocation (step 1612). The metrology system 202 can be placed on asupport structure 224 placed on the seabed, carried by an ROV or AUV 216that is stationary on the seabed, carried by an ROV or AUV 216 that isfloating in a station-keeping mode, carried by an ROV or AUV 216 that isfloating but latched on (through manipulators or other device) to astructure on the seabed for stability, or otherwise carried or placed inthe vicinity of the acoustic transponders 228.

The next step is to locate metrology system 202 in relation to the field100 (step 1616). Information regarding the location of the monitoringsystem 202 can be provided by the INU 403. Alternatively, or inaddition, the monitoring system 202 can obtain information regarding itslocation by referencing one or more geo-located monuments 226 or otherstationary structures on the seabed, or even by the seabed featuresthemselves. Location information obtained relative to the geo-locationmonuments 226 can replace or be supplemented by the known location ofthe metrology system 202, obtained, for example, from an INU 403, orother stationary structures on the seabed such as target stands 222,manifolds 128, wells 130, or suction piles 136, or even by the seabedfeatures themselves. Note the location can be geo-referenced or can be alocation that is relative to locations of the structures on the seabed.

A 3-D point cloud that includes acoustic transponders 228 is thencreated using the lidar device 308 included in the metrology system 202(step 1620). With a known location of metrology system 202, this pointcloud can be put in global or georeferenced coordinates so the locationof indicia 512 is known in georeferenced X, Y, Z space. Alternately, thelocation can be relative to a specific structure or feature, or relativeto the monitoring system itself. In an additional embodiment, the pointcloud includes both the transponders 228 and monuments 226. The relativelocations of the acoustic transponders 228 are then determined in 3Dspace (X,Y,Z, roll, pitch, yaw coordinates) with respect to one or moreof the monuments 226 (step 1624). The DC offsets for each of theacoustic transponders 228 can then be applied to identify the locationof the acoustic element 516 of each acoustic transponder 228 in 3D space(step 1628). The process can then end.

FIG. 17 depicts an undersea scenario including multiple monitoringsystems 202 exchanging location information with one another via acommunication link 1704 established in accordance with embodiments ofthe present disclosure. The use of multiple monitoring systems 202 canbe advantageous, for example where the desired field of coverage isrelatively large. In such a scenario, the monitoring systems 202 canadvantageously exchange location information with one another. Inaccordance with embodiments of the present disclosure, the differentmonitoring systems 202 can identify and locate one another using indicia512, such as targets 240 and/or 244, placed on exterior surfaces of themonitoring systems 202.

With reference now to FIG. 18, aspects of the operation of a combinedsystem 200 in accordance with embodiments of the present disclosure,where multiple metrology systems 202 are included, as depicted in FIG.17, are illustrated. In this example, at step 1804, a metrology systemis placed in an underwater field in which a monument 226 and acoustictransducers 228 have already placed. At step 1808, a determination ismade as whether any additional metrology systems 202 are to be placed inthe field. In this example, at least two metrology systems 202 will beplaced in the scene. After all of the desired metrology systems 202 arein place, the metrology systems are operated to generate point clouddata (step 1812). Individual acoustic transponders 228 and/or monuments226 within the different sets of point cloud data generated by thedifferent metrology systems 202 can then be identified, and theirlocations can be determined (step 1816). Note the unique identifyingmarks on transponders 228, monuments 226, or other objects 102 caninclude a bar code type system that the optical system automaticallyreads. The system can then use a database to identify the uniquetransponder, monument, or structure and acquire the DC offsets or othermetadata from a database, such as exact hub number, installation date,etc. This not only provides additional information, but also reduces theneed for ROV video identification.

The location information regarding the identified acoustic transponders228 and monuments 226 can then be exchanged between the metrologysystems 202 (step 1820). The information can be exchanged through adirect acoustic link between the different metrology systems, forexample established by the included acoustic transceivers 310. Asanother example, the information can be exchanged through a relay, suchas through a monitoring and control station. As a further example theinformation can be exchanged by optical communications. In addition, thepoint cloud data and/or location information determined by the metrologysystem 202 can be communicated to a monitoring and control station 804or other combined system 200 node. The monitoring and control station804 or other node can then stitch together the data to provide a widearea set of 3-D location information. The process can then end.

Subsea structures 102 can have acoustic transponders 228 located onthem, along with DC information that locates the acoustic transponder228 onto the structure. The subsea structure is then located within theacoustic array comprising the set of multiple, for example as depictedin FIG. 15, four, acoustic transponders 228, by the acoustictransponders 228 pinging range and possibly azimuth and elevationangular information to each other. Many more acoustic transponders 228are normally used to increase the accuracy of the array and to provideredundancy when power goes low (batteries die) on the acoustictransponders. The solution for the location of the subsea structureacoustic transponder can be calculated on the surface.

By including a metrology system 202 having an active optical system, thelidar device 308, in the field 100, several advantages are obtained.First, a lesser number of acoustic transponders 228 can be used ascompared to a classic arrangement in which only acoustic locationinformation is utilized, because the lidar device 308 of the metrologysystem 202 can be used to locate (geo or relative) the acoustictransponders 228 with respect to on another more accurately than can bedone using acoustic transponder 228 alone. Also, the metrology system202 can be used to locate the subsea structures 102 using opticaltargets 240 on the structures 102. The locations of the acoustictransponders 228 and the locations of the structures 102 obtained by theacoustic system and obtained by the optical system can then be sent to acentral processing center either underwater or topside. The acoustic andoptical results can be compared for accuracy and redundancy.

For instance, if an acoustic transponder 228 ran out of batteries orwent bad, the metrology system 202 can still give that transponder's 228location to the array or remaining, active acoustic transponders 228. Inreverse, if water visibility turned poor due to a storm or currents orsubsea operations that stirred the seabed, and the range of the opticalmonitoring system 308 was decreased, the acoustic system can then beused or weighed higher in the combined data.

The inclusion of a metrology system 202 within a field of multipleacoustic transponders 228 can provide for more accurate angular anddistance measurements between the included objects, including theacoustic transponders 228, as compared to scenarios in which acoustictransponders 228 are used without a light based measuring system.Alternatively or in addition, fewer acoustic transponders 228 may beused across the field, as compared to scenarios in which a light basedmeasurement system 308 is not included. The range and angle measurementscan further be improved by including one or more geo-located monuments226.

FIG. 19 depicts a 3-D target 240 in accordance with embodiments of thepresent disclosure, and FIG. 20 depicts a 2-D target 244 in accordancewith embodiments of the present disclosure. The targets 240 and 244 caninclude shapes that assist a metrology system 202 in determining arelative orientation of the target 240 and 244, and the associatedobject 102, monument 226, target stand 222, or acoustic transponder 228.The target 240 or 244 can additionally include identifying markings 1904that allow the target 240 or 244 and/or the associated object 102,monument 226, target stand 222, or acoustic transponder 228 to beuniquely identified. Moreover, the identifying markings 1904 can allow asurface, component, or other feature of an object 102 to which thetarget 240 or 244 is mounted or applied to be identified. Note theunique identifying marks on transponders 228, monuments 226, targetstand 222 or other objects 102 can include a bar code type system thatthe optical system automatically reads. The system can then use adatabase to identify the unique transponder, monument, target stand orstructure and acquire the DC offsets or other metadata from a database,such as exact hub number, installation date, etc. This not only providesadditional information, but also reduces the need for ROV videoidentification. In accordance with further embodiments of the presentdisclosure, the target 244 may comprise a three-dimensional target thatprovides the shapes 1904 in the form of the physical shape of the target244. A target 244 in the form of a three-dimensional object mayadditionally include two-dimensional shapes or identifying markings1904. A target 240 can also be provided in the form of an entirelytwo-dimensional shape and/or identifying markings 1904. In accordancewith still other embodiments of the present disclosure, a target 240 or244 can modify a polarization, amplitude, phase, and wavelength, orother attribute of incident light that is received from and reflectedback to a metrology system 202. In another example, a target 240 or 244may comprise one or more prisms. In accordance with further embodimentsof the present disclosure, the target 240 or 244 can include a hologramthat modifies light received from a metrology system 202 to produce aparticular pattern.

In an additional embodiment, an acoustic transponder 228 can be uniquelyidentified by a laser metrology system 202 by using the opticalmetrology system 308 of the metrology system 202 to measure thevibration signature of the acoustic transducer 516. In particular, ifeach acoustic transponder 228 has a unique acoustic code it transmits, alaser monitoring system can detect this unique code by operating thelidar device 308 to dwell along a line of sight to the acoustictransponder 228, and in particular the acoustic transducer 516 of theacoustic transponder 228, to optically measure the vibration and thussignal of the transducer 516.

In accordance with embodiments of the present disclosure, a combinedsystem 200 utilizes both acoustic and optical information to locateobjects 102 in an underwater environment. A metrology system 202provided as part of the combined system 200 can thus include a lidardevice 308 to obtain precise, optically derived location and rangeinformation for targets 240 or 244. From relative location informationobtained by optically detecting targets 240 or 244 associated with ageoreferenced monument 226 or other georeferenced structure or object102, the metrology system 202 can determine the geolocation of otherobjects 102, including by not limited to acoustic transponders 228. Thecombined system 200 can also use acoustic methodologies for determininglocation. For instance, an initial, relatively coarse location may bedetermined using the acoustic transceiver 310 of a metrology system 202.That initial location can be used to assist the metrology system 202 inpointing the lidar device 308 toward optical targets 240 or 244associated with a georeferenced monument 226 or structure 102. Inaddition, precise, optically derived location information for anacoustic transponder 228, and in particular of the acoustic transducer516 of the acoustic transponder 228 can be determined using the lidardevice 308 of the metrology system 202. Location information derivedfrom an acoustic output of the acoustic transponder can then be moreaccurate, since the location of the emitting acoustic transponder 228 isitself more accurately determined than if acoustic signals alone wereused to locate that acoustic transponder 228. In accordance with stillother embodiments of the present disclosure, acoustic and optical signalmethodologies are combined simultaneously. For instance, a lidar device308 can dwell for a period of time along a line of sight that intersectsthe surface of an acoustic transducer 516 included as part of anacoustic transponder 228. A frequency or modulated frequency output bythe acoustic transducer 516 as an identification signal can then bedetected using the lidar device 308. Moreover, by pointing the lidardevice 308 at a particular acoustic transponder 228 emitting anidentification signal, the identity and location of that acoustictransponder 228 can be determined with certainty. This can be useful invarious scenarios, for example where noise in the underwater environmentmakes identifying a particular acoustic transducer 228 using theacoustic signal alone difficult.

Embodiment of the present disclosure further support the reliablelocating of objects 102 in an underwater environment in variousconditions and over large areas. Moreover, the combined system 200described herein provides for the integration of acoustic and opticallocating methodologies. For instance, a first metrology system 202within sight of a georeferenced monument 226 can determine a geolocationof an acoustic transponder 228 also within sight of the metrology system202 with great accuracy. This provides location information derived atleast in part from an acoustic signal output from the opticallygeolocated acoustical transponder 228 to be more accurate than if itwere only acoustically geolocated. In addition, the use of opticallocating methodologies enables the use of accurate, three pointresection traverses, which in turn allows the location of underwaterstructures 102 to be determined accurately.

In addition, by also including acoustic technologies, some level oflocation information can be provided even when the water within theenvironment is turbid. For instance, where turbidity and/or thedistances between underwater objects 102 preclude the use of opticalmetrology techniques over the entire underwater area or scene, ametrology device 202 at one or both ends can utilize optical techniquesfor precisely locating other underwater objects 102 within the range ofthe lidar device 308, while acoustic devices can provide locationinformation for other segments of a chain of located objects 102.

As a specific example, consider a classic underwater spool piecemetrology where a pipe section is needed to connect a well head to amanifold. The hubs on each end are the connection points for theconnecting pipe. Key pieces of information required for building thiscustom pipe are the slope distance between hubs as well as relativeinclinations from one hub to another in both pitch and roll. Otherrequirements are, relative heading, and height above seabed for eachhub. Sometimes the seabed profile is also required.

In several instances the optical system alone can perform thismeasurement. However, if the pipe distance is extremely long, forinstance 100 meters, or water clarity is poor, then the optical systemalone is not optimal. In this scenario, acoustic transponders are placednear the hubs at each end. The metrology device 202 is then used at eachhub to measure pitch, roll, heading, height above seabed, surroundingseabed profile, and acoustic transponder 228 locations near each hub.The distance between hubs is then calculated using the acoustictransponder 228 information from each end. The point clouds from eachend are basically tied together into a common reference frame by theacoustic transponder data.

In a further embodiment, the above processes can be performed with anoptical system alone using two different reflectivity levels for targets240 or 244, on the objects 102, or in conjunction with the acousticsystem as a back-up or validation. In this scenario, highly opticallyreflective targets and standard targets 240 or 244 are placed on theobjects 102 at the surface and dimensional control data is acquiredbetween all the targets. The objects and metrology system are thenplaced subsea. The subsea metrology device 202 is placed near one of thestructures and a full scan of the object is taken at a normal gainsetting, which will produce saturated data for the highly reflectivetarget. This point cloud dataset will include the standard reflectivitytargets along with the structure itself and potentially surroundingseafloor, so it is a complete point cloud dataset with information ontargets and structures. Before moving the metrology system, a very lowgain scan is also performed which allows for the highly reflectivetargets to not be saturated. This dataset will capture limited or noreturns from the standard reflectivity targets, the structure, orseafloor. Therefore it is not a complete point cloud but rather adataset with only the highly reflective target returns, Since the twoscans were acquired from the same metrology system location, they can bemerged into a common point cloud. In another embodiment, the highlyreflective targets are placed after the object is underwater or isplaced on target stands 222 near the object 102.

The metrology system 202 then pans over in the direction of the otherhub and performs a high-level scan. The only object that will be visibleto the metrology device are the highly reflective targets. Therefore theresulting point cloud contain no information on the standard targets orobjects or seabed. However, since DC data was taken topside the entirestructure can be located using the highly reflective targets. The sameoperation can be performed at the other hub for redundancy and to obtainpitch, roll, heading, height above seabed, and seabed profileinformation for the second hub from the standard scan. As an additionalembodiment, the metrology system 202 is placed approximatelymid-distance between the two hubs and only the highly reflective targets240 or 244 are captured from each hub, but both are captured from thesame scan location. This can be performed as another redundancy step anddata check.

A highly reflective target is any target 240 or 244 that gives an almostmirror like return, such as a survey prism, other prism,retro-reflectors, mirror, reflective tape, reflective paint,micro-spheres, and other micro objects or shapes that can be embedded inpaints, tapes, and materials in order to produce retro-reflections orvery high signal returns.

In accordance with at least some embodiments of the present disclosure,the technology encompasses:

(1) A method for locating objects underwater, comprising:

placing a first metrology device at a first approximate location;

operating an optical metrology system provided as part of the firstmetrology device to determine a location of the first metrology devicerelative to an object having a known location;

placing a first acoustic transponder at a second approximate location;

operating the optical metrology system of the first metrology device todetermine a location of the first acoustic transponder relative to theknown location.

(2) The method of (1), further comprising:

prior to placing the first acoustic transponder at the secondapproximate location, applying a target to the first acoustictransponder, and determining dimensional control data concerning arelationship between the applied target and an acoustic transducer ofthe first acoustic transponder.

(3) The method of claim (1) or (2), further comprising:

operating the first acoustic transducer to output at least one of anidentification and a ranging signal.

(4) The method of any of (1) to (3), further comprising:

operating the optical metrology system of the first metrology system topoint at the acoustic transducer of the first acoustic transponder overtime and to measure a vibration of the acoustic transducer and thusacquire the acoustic signal output from the acoustic transponder whilethe optical metrology system is pointed at the acoustic transducer.

(5) The method of any of (1) to (4) wherein an optically reflectivetarget is placed on a center point of the acoustic transducer.

(6) The method of any of (1) to (5), wherein the object has targets andindicia, and wherein the indicia allows for unique identification toaccess metadata on the object such as offsets, hub number, and date ofinstallation.

(7) The method of any of (1) to (6), wherein the object is geolocated,and therefore the first metrology system and the first acoustictransponder can be geolocated.

(8) The method of any of (1) to (7), wherein an acoustic array andinertial navigation unit (INU) system are used to geolocate the firstmetrology system and the first acoustic array.

(9) The method of any of (1) to (8), further comprising:

determining a range between the acoustic transducer placed at the secondapproximate location and another acoustic transducer.

(10) The method of any of (1) to (9), further comprising:

communicating the determined location of the first acoustic transponderfrom the first metrology system to the first acoustic transponder; and

storing the determined location of the first acoustic transponder on thefirst acoustic transponder.

(11) The method of (10), further comprising:

placing a second acoustic transponder;

communicating the determined location of the first acoustic transponderto the second acoustic transponder.

In accordance with still further aspects of the present disclosure, thetechnology encompasses:

(12) A system for locating objects underwater, comprising:

a plurality of acoustic transponders, the acoustic transponders eachincluding:

-   -   an acoustic transducer;    -   indicia, wherein dimensional control information concerning a        relationship between the acoustic transducer and the indicia is        known;

a metrology system, the metrology system including:

-   -   a light source;    -   a receiver; and    -   a processor, wherein the processor operates the light source to        generate light that is directed towards a first acoustic        transponder included in the plurality of acoustic transducers,        reflected from the first acoustic transponder, and received at        the receiver to determine a location of the first acoustic        transponder relative to the metrology system.

(13) The system of (12), wherein an acoustic transducer of the firstacoustic transponder, in a first operating mode, generates anidentification signal.

(14) The system of (12) or (13), wherein the metrology system isoperable to detect the identification signal of the first acoustictransponder using the light source and the receiver.

(15) The system of any of (12) to (14), wherein the metrology systemfurther includes an acoustic transceiver.

(16) The system of any of (12) to (15), wherein the indicia includestargets placed on the acoustic transponders.

(17) The system of any of (12) to (16), wherein the indicia allows forunique identification to access metadata on the object such as offsets,hub number, and date of installation.

(18) The system of any of (12) to (17), wherein the indicia are similarto a bar code system that is read by the optical system.

(19) The system of any of (12) to (18), wherein the locations of theplurality of transponders and the plurality of metrology systems are allshared and stored at a central processing center.

In accordance with still further aspects of the present disclosure, thetechnology encompasses:

(20) A method for locating objects underwater, comprising:

determining a location of a plurality of acoustic transponders;

for at least a first acoustic transponder included in the plurality ofacoustic transponders, storing the determined location in memoryincluded in the first acoustic transponder;

communicating a location of the first acoustic transponder from thefirst acoustic transponder to a second acoustic transponder included inthe plurality of acoustic transponders.

(21) The method of (20), wherein determining a location of a pluralityof acoustic transponders includes determining a location using anoptical metrology system.

(22) The method of (20) or (21), wherein the first acoustic transponderincludes a first target and a first acoustic transducer, the methodfurther comprising:

determining dimension control information regarding a location of thefirst target relative to a center of the first acoustic transducer.

In accordance with still further aspects of the present disclosure, thetechnology encompasses:

(23) A method for performing a long-distance metrology, comprising,

placing both low and high reflectivity targets on a structure;

taking dimension control (DC) data of the targets and the structure;

placing a first metrology system at a first location close to at least afirst portion of the structure and performing first and second scans ofthe structure, wherein the first scan is at a standard gain level tocapture a first point cloud that includes returns from the structure,low reflectivity targets, and seabed, wherein the second scan is at alow gain level to capture a second point cloud that includes returnsfrom the high reflectivity targets.

(24) The method of (23), further comprising:

placing one of the first metrology system and a second metrology systemat a second location close to at least a second portion of the structureand performing third and fourth scans of the structure, wherein thethird scan is at a standard gain level to capture a third point cloudthat includes returns from the structure, low reflectivity targets, andseabed, wherein the fourth scan is at a low gain level to capture afourth point cloud that includes returns from the high reflectivitytargets.

(25) The method of (24), further comprising:

locating at least some of the high reflectivity targets in the returnsin both the second and fourth point clouds;

combining the first and third point clouds using the at least some ofthe high reflectivity targets in the returns in both the second andfourth point clouds as control points.

(26) The method of any of (23) to (25), wherein the long range datacollected from the high reflectivity targets are cross-checked withacoustic transponder data across the same distance.

The foregoing discussion has been presented for purposes of illustrationand description. Further, the description is not intended to limit thedisclosed systems and methods to the forms disclosed herein.Consequently, variations and modifications commensurate with the aboveteachings, within the skill or knowledge of the relevant art, are withinthe scope of the present disclosure. The embodiments describedhereinabove are further intended to explain the best mode presentlyknown of practicing the disclosed systems and methods, and to enableothers skilled in the art to utilize the disclosed systems and methodsin such or in other embodiments and with various modifications requiredby the particular application or use. It is intended that the appendedclaims be construed to include alternative embodiments to the extentpermitted by the prior art.

What is claimed is:
 1. An underwater system, comprising: an underwatertarget, including: an optical target; and indicia uniquely identifyingthe underwater target.
 2. The system of claim 1, further comprising: anobject, wherein the underwater target is fixed to the object.
 3. Thesystem of claim 2, further comprising: an optical metrology system,wherein the optical metrology system determines a location of theunderwater target within an underwater environment.
 4. The system ofclaim 3, wherein the optical metrology system includes a communicationsystem to transmit the determined location of the underwater target toanother system component.
 5. The system of claim 4, wherein the othersystem component is the object to which the underwater target is fixed.6. The system of claim 5, wherein the object is moving within theunderwater environment.
 7. The system of claim 6, wherein the object isa vehicle, and wherein the vehicle is assisted in navigating theunderwater environment.
 8. The system of claim 3, wherein the opticalmetrology system is carried by a vehicle.
 9. The system of claim 1,wherein the underwater target further includes an acoustic transducerthat is provided as part of an acoustic transponder.
 10. The system ofclaim 9, wherein the acoustic transponder is mounted to a vehicle. 11.The system of claim 10, further comprising: an optical metrology system,wherein the optical metrology system determines a location of theacoustic transducer within an underwater environment, and wherein theoptical metrology system includes a communication system to transmit thedetermined location of the underwater target to a component carried bythe vehicle.
 12. An underwater target, comprising: an optical target;and indicia uniquely identifying the underwater target.
 13. Theunderwater target of claim 12, wherein the indicia is integral to theoptical target, and wherein the optical target modifies at least one ofa polarization, amplitude, phase, or wavelength of light.
 14. Theunderwater target of claim 13, wherein at least one of the opticaltarget or the indicia is a hologram.
 15. The underwater target of claim12, further comprising: an acoustic transducer, wherein the acoustictransducer forms at least a portion of an exterior of the underwatertarget, and wherein the optical target is formed on a surface of theacoustic transducer.
 16. The underwater target of claim 15, furthercomprising: a housing; a processor located within the housing; memorylocated within the housing, wherein a location of the underwater targetis stored in the memory; and a power supply located within the housing,wherein the processor is operable to execute instructions stored in thememory to transmit the location using acoustic signals output by theacoustic transducer.
 17. The underwater target of claim 12, furthercomprising: a plurality of optical targets, wherein at least some of theoptical targets are in different orientations from one another, whereinat least one of the optical targets is a three-dimensional (3-D) target.18. The underwater target of claim 12, further comprising: at least oneof a housing or a monument; and a plurality of optical targets, whereinat least some of the optical targets are connected to and spaced apartfrom the at least one of a housing or a monument by an arm, and whereinat least some of the optical targets are in different planes.
 19. Theunderwater target of claim 18, wherein the underwater target includes amonument, the underwater target further comprising: a scale on a surfaceof the monument.
 20. A method of locating objects in an underwaterenvironment, comprising: providing an underwater target having aplurality of optical targets and identifying indicia; taking dimensioncontrol data of the underwater target; storing the dimension controldata in a database; placing the underwater target in the underwaterenvironment; locating the underwater target within the underwaterenvironment; identifying the underwater target within the underwaterenvironment from the identifying indicia; and storing the location ofthe underwater target within the underwater environment in memoryincluded as part of the underwater target.